Illustrator Tutorial - Opacity Masks

If you've used Photoshop, you may be familiar with 'masks'.  If not, don't worry.  We'll explain what they are in Illustrator.

Opacity Masks reveal what lies underneath them depending on the Luminosity values of the fill of the path that is used as a Mask. This means that depending on how light or dark the mask is, will adjust the visibility of the image below.

We'll start with an image - it can be a photo, vector art, text etc.

Next, using the Rectangle Tool  we've drawn a rectangle, copied it and pasted the copy three times.  Drag them into position and fill two with white and two with black, group the four rectangles (OBJECT...Group) and make sure this 'grid' is above the original image (OBJECT...Arrange...Bring to Front) - all as below:

Now, using the Selection Tool , drag a marquee across all the elements to select them.  Make sure your Transparency palette is visible (WINDOW...Transparency)

Click on the tiny black 'drop down' arrow and choose 'Make Opacity Mask'.

As you see, the Opacity Mask has been succesfully applied and the photograph has been clipped to the outer dimensions of the grid. Since it's all based in Luminosity, and since you can not get any lighter color than White, the parts of the photograph that lie underneath the white areas of the grid will be fully visible (100% opaque - can not see through). On the other hand, areas of the photograph that lie underneath the black rectangles are no longer visible - they have become transparent (0% Opacity - can see through). This means that any object you place behind the photograph will be visible on these areas.

Above is the Transparency palette after we've applied the Opacity mask. You'll notice that there are two thumbnails available (ITEMS 1 & 3), one showing the photograph (ITEM 1) and one showing the mask (ITEM 3) with a lock icon in between (ITEM 2). By default the photo and the mask are locked together and what this does is that if let's say you decide to move the photo, then the mask is moved together. If for some reason you want to move the photograph but you do not want to move the mask (maybe you want to show another part of the photo), then click on the lock icon (it disappears...) and reposition the photo. The mask will stay in place.

Checking 'Invert Mask' (5) will 'swap' the black and white elements of the mask over.

So you can see, some interesting effects can be achieved by using solid blocks of black and white (although there are other ways of doing this in Illustrator), but nothing like the effects we can get by using gradients.

Now let's look at Opacity Masks using gradients next>>>

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